By Whitney Cranshaw, Colorado State University Cooperative Extension
specialist, entomology

Spectacular swarms of flying ants are a common summer phenomenon. Sometimes people will
observe winged ants issuing in large numbers, pushed out by the wingless workers, from a
colony established between a sidewalk crack or in a small mound. Other times only the
winged forms will be seen, aggregating in large numbers around certain prominent points in
the landscape.

Some background. Ants are social insects. The colony is established through the initial
efforts of a mated "queen", a sexually mature female. Originally winged, after
mating she sheds her wings and the no longer used wing muscles are an important source of
nutrients for her during the early stages of colony development. Very, very few queens
successfully survive this period and establish a functional colony.

However, if the colony makes it through this period it can begin to grow. Wingless,
non-sexually mature workers are reared which
subsequently help expand the colony. After several years, the colony may be
well-established and then some resources are put into rearing reproductive forms. These
are the winged ants, some females - the potential future queens - and the majority males.

Periodically, usually following by 3-5 days a heavy rain, the winged reproductive forms
emerge from the colony in large swarms. Such swarming behavior is usually synchronized by
other nearby colonies so large numbers of winged ants suddenly appear. All mating for the
species takes place, often over the course of a single day. The males die and the mated
females disperse to attempt establishing a new colony.

One behavior associated with some ants during mating swarms is "hilltopping".
This refers to their aggregation around prominent points of a landscape where they search
for mates. A large tree, the chimney of a roof or even a tractor moving across the plains
might serve as such an "action site" for swarming winged ants. My favorite
hilltopping site was the top of the US West tower in downtown Denver, which annually is
the site for millions of harvester ants to aggregate.

Although dramatic, swarming ants pose no harm or risk of increased ant infestation.
Those seen emerging from a colony were always there and are in the process of leaving the
colony permanently. Mated females amongst aggregating masses similarly disperse from the
area.

However, in rare cases winged ants are seen moving into the house. In some cases it is
likely that an established colony exists within the home and may need to be treated.
Carpenter ants and pharaoh ants are two species that can produce a nest within a building.

Other ants, such as the field ants, commonly nest outdoors next to foundations and may
incidentally swarm indoors, working their way indoors through foundation cracks. And
harvester ants in the midst of hilltopping behavior may fall down chimneys. In these cases
there is not risk of permanent household infestation.